Alternator or battery?

[Brahmajoe]

I posted on this also. This weekend I traveled for 2 hrs to the beach , the lowest the gauge read was 14.2. when I got there , the next morning I drove for 45 min, gauge read 1
14,5, Stopped for coffee, restarted and gauge read 14 .1 . The next day 2 hr drive home and gauge went between 14.5 and home at 14.1. This morning , started at 14. 7 then down to 14.4. Are these readings showing that the batteries are weak. Other than that , I have no problems with the Glad at all, no elec or running problems. I would just hate to be on the beach and it will go dead . This would be a tremendous tow bill. Lol

I just always thought the higher the reading the more the alternator was powering up the battery. My wife’s stays at a nice 13.5 while driving. What yours say with key on engine off?

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[Hunter#1]

Yes I did do that, it read 12.7 . Is that good ? Like I said I'm having no problems, I'm just a worry warth. You know how cars and trucks are, they break down at very bad times.

 

[ShadowsPapa]

I posted on this also. This weekend I traveled for 2 hrs to the beach , the lowest the gauge read was 14.2. when I got there , the next morning I drove for 45 min, gauge read 1
14,5, Stopped for coffee, restarted and gauge read 14 .1 . The next day 2 hr drive home and gauge went between 14.5 and home at 14.1. This morning , started at 14. 7 then down to 14.4. Are these readings showing that the batteries are weak. Other than that , I have no problems with the Glad at all, no elec or running problems. I would just hate to be on the beach and it will go dead . This would be a tremendous tow bill. Lol

Find out what the voltage is at the battery when the truck is off, just sitting there, fob well out of range. When the fob is in range, other things power up and there's more draw. Checking it sitting stopped in a driveway or garage with no fob nearby will give a better read on the batteries. Even fully charged, they'll read lower than 12.7 or 12.8 after the truck sits due to the draw on the batteries at all times.
But mine, as I've said - when fully charged, 100%, after sitting over 14 hours still read 12.66 volts.

 

[Brahmajoe]

That is a good number. I think 12.6 is what you want. I’m 12.2 12.3ish and drive it often

 

[ShadowsPapa]

I just always thought the higher the reading the more the alternator was powering up the battery. My wife’s stays at a nice 13.5 while driving. What yours say with key on engine off?

13.5 means the batteries are seen by the system as not too low, just needing a slight fill-up. Watch when going down a hill, foot off the gas, or even braking a bit - a fully charged, healthy pair of batteries you'll see the voltage drop to about 12.8 volts then when you apply gas again, it will go back up a bit into the 13s.

 

[ShadowsPapa]

That is a good number. I think 12.6 is what you want. I’m 12.2 12.3ish and drive it often

The old wet cell batteries were fully charged, 100%, at about 12.66 volts.
The AGM batteries used in vehicles today, like our Jeeps, are fully charged at roughly 12.7-12.8

If the batteries were 100% state of charge and healthy, you'll see 12.6 or so after just a few hours of sitting due to the draw on the batteries. If you disconnected them, that may rise back up a bit because the constant tiny draw on the batteries lowers the voltage you read while they are connected in the truck.

 

[Hunter#1]

Thanks all, I'll try it tonight without the key fob near. I'm getting my first oil and filter change this Saturday before I leave for the beach. I'm getting it changed at 2k, then 5 k every time after that. I'm learning a lot from this forum and its members.

 

[Hunter#1]

I tried it with out the key farb. It wouldn't do anything with out the farb. But when I got the farb and put if on acc , the battery gauge read 12.7 and stayed there. Is that a good sign ?

 

[Brahmajoe]

I tried it with out the key farb. It wouldn't do anything with out the farb. But when I got the farb and put if on acc , the battery gauge read 12.7 and stayed there. Is that a good sign ?

Yes

 

[Brahmajoe]

The half hour drive home voltage was at a steady 14.2 volts

 

[20Silver20]

I’m not sure if this is the correct spot for my question. 2020 Gladiator purchased used in Nov 23. On day two of my return trip from Colorado to Texas I noticed that I wasn’t getting the usual airflow from the vents. I cycled through the info screens to check temperature, voltage etc. at 75mph my voltage was 12.7. When I would coast or brake it would go up towards 14volts. I stopped and took a look under the hood. Nothing seemed out of the ordinary. I still felt less than normal airflow. After getting home I let it sit for a couple of hours. The airflow improved but the voltage readings were the same. Voltage readings were the same this morning. I have had no issues with the JT.
I was wondering if these voltage levels are normal?

Summary: 12.7 volts while driving and increasing to around 14 volts while stopping then back to 12.5-12.7 while stopped.
Thanks

 

[ShadowsPapa]

I’m not sure if this is the correct spot for my question. 2020 Gladiator purchased used in Nov 23. On day two of my return trip from Colorado to Texas I noticed that I wasn’t getting the usual airflow from the vents. I cycled through the info screens to check temperature, voltage etc. at 75mph my voltage was 12.7. When I would coast or brake it would go up towards 14volts. I stopped and took a look under the hood. Nothing seemed out of the ordinary. I still felt less than normal airflow. After getting home I let it sit for a couple of hours. The airflow improved but the voltage readings were the same. Voltage readings were the same this morning. I have had no issues with the JT.
I was wondering if these voltage levels are normal?

Summary: 12.7 volts while driving and increasing to around 14 volts while stopping then back to 12.5-12.7 while stopped.
Thanks

Normal, especially on a long trip and even more especially when it's hot outside and the battery gets hot.

 

[20Silver20]

Normal, especially on a long trip and even more especially when it's hot outside and the battery gets hot.

Thanks for the info. This was my first long trip with the JT and it was definitely hot outside.

 

[BaliMawr]

Ok, looking for some clarity- I just had both batterie$ replaced, so naturally, I’m watching the voltmeter, because I had NO warning that they were going. I seem to remember that a few weeks ago, I noticed the voltmeter was in the 14s, and I thought that was good. Now, with the new batteries, it’s barely breaking 12.8 on the highway, generally going up when I show, which is opposite of what I expect. Am I correct in understanding (after reading here) that the volt reading in the dash is not alternator output but battery demand? So the fact that I’m seeing low numbers means the batteries are good, and the fact that it gots up when slowing is because alternator output is reduced? It sounds like this is what’s happening, but I haven’t seen anyone say it like that directly. Thanks!

 

[ShadowsPapa]

Ok, looking for some clarity- I just had both batterie$ replaced, so naturally, I’m watching the voltmeter, because I had NO warning that they were going. I seem to remember that a few weeks ago, I noticed the voltmeter was in the 14s, and I thought that was good. Now, with the new batteries, it’s barely breaking 12.8 on the highway, generally going up when I show, which is opposite of what I expect. Am I correct in understanding (after reading here) that the volt reading in the dash is not alternator output but battery demand? So the fact that I’m seeing low numbers means the batteries are good, and the fact that it gots up when slowing is because alternator output is reduced? It sounds like this is what’s happening, but I haven’t seen anyone say it like that directly. Thanks!

The voltage reading is actually what the alternator is putting out. It's based on what the battery and rest of the truck needs. If the IBS reports that the batteries need to be topped off, the voltage will rise. If the batteries are full or hot, the voltage drops.
Normally the voltage will read lower while there's demand for power from the engine, and higher when the load is low (like coasting or going down a hill.)
I call the voltage "system voltage" - as it's what you would read on almost any wire tied to the alternator or batteries.

Sounds to me like yours is working fine.
After you start it, the batteries will be low due to the drain of starting. The IBS reports what was taken out, and the system tries to balance that and put back in - but will adjust based on engine load at times.

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